In recent years, positioning of position coordinates of many locations uses a global navigation satellite system (global navigation satellite system).
In the Global Positioning System (GPS), which is a representative global navigation satellite system, position coordinates of a GPS receiver (positioning terminal) can be determined through use of a plurality of GPS signal waves transmitted from a plurality of GPS satellites (NAVSTARs).
With a positioning method using the GPS signals, as a result of various researches and developments, a current position (position of positioning terminal) can now be determined by the terminal alone almost in real time with an accuracy of about 10 m. This real-time positioning uses a broadcast ephemeris superimposed on the GPS signal.
Further, as a positioning method for enhancing a positioning accuracy, there are a positioning method using a precise ephemeris and a positioning method involving causing a plurality of terminals to operate in cooperation with one another. The precise ephemeris is obtained by, for example, the International GNSS Service (IGS) by calculating a precise route of a satellite orbit. Through use of this precise ephemeris indicating the precise route in combination with other methods, a positioning terminal, although not being able to perform the real-time positioning, can enhance its positioning accuracy to about 10 cm.
Technologies, which are related to the broadcast ephemeris and the precise ephemeris, are disclosed in, for example, Patent Documents 1 to 3.
In Patent Document 1, there is disclosed a GPS positioning system configured to perform high-accuracy positioning through use of the final ephemeris controlled by the IGS. Further, in Patent Document 1, there are descriptions of a rapid ephemeris and the final ephemeris.
In Patent Document 2, there is disclosed a GPS positioning system configured to perform high-accuracy positioning through use of the final ephemeris controlled by the IGS. In this system, as long as data is collected at the same location for about 24 hours for positioning, a positioning accuracy in the order of centimeters is obtained.
In Patent Document 3, there is disclosed a global navigation satellite system capable of reducing, when a positioning terminal executes positioning that is based on a plurality of navigation signals, a period of time required for processing to be performed prior to the start of calculation of generating pseudoranges to respective satellites (calculation processing of causing various numerical values to converge). In the method disclosed in this document, a signal propagation time of an arbitrary satellite that can be determined first is used for calculation of a signal propagation time of another satellite.